This invention relates to a circuit arrangement for operating a semiconductor light source comprising
connection terminals for connecting a control unit, PA1 input filter means, PA1 a converter having a control circuit, PA1 output terminals for connecting the semiconductor light source, PA1 means CM for removing a leakage current occurring in the control unit in the non-conducting state, which means include a controlled semiconductor element, and PA1 self-regulating deactivating means for deactivating the means CM.
The invention also relates to a signalling light provided with such a circuit arrangement.
A circuit arrangement of the type mentioned in the opening paragraph is described in U.S. Pat. No. 5,661,645. Semiconductor light sources are increasingly used as signalling lights. In such an application, a semiconductor light source has an advantage with respect to the usual incandescent lamp in that it has a much longer service life and a considerably lower power consumption than an incandescent lamp. Signalling lights often form a part of a complex signalling system, for example, a traffic control system with traffic lights. If the above advantages of semiconductor light sources are to be effected on a wide scale, it is necessary for the circuit arrangement to provide retrofit possibilities with respect to existing signalling systems.
A signalling light in an existing signalling system is often controlled by means of a solid-state relay, a status test of the relay and of the signalling light taking place at the connection terminals of the connected circuit arrangement. It is a general property of solid-state relays that a leakage current occurs in the non-conducting state of the relay. To preclude an incorrect outcome of the status test during operation of a semiconductor light source, use is made of the means CM which ensure that, in the non-conducting state of the control unit, for example a solid-state relay, a leakage current occurring in the control unit is removed and that the voltage at the connection terminals of the circuit arrangement remains below a level necessary for obtaining a correct outcome of the status test. It is thus achieved, in a simple and effective manner, that the circuit arrangement exhibits a characteristic at its connection terminals which corresponds substantially to the characteristic of an incandescent lamp. In this respect, an important feature of an incandescent lamp characteristic is the comparatively low impedance of the lamp in the extinguished state, so that the removal of the leakage current through the incandescent lamp leads only to a low voltage at the connection terminals of the control unit. The means CM include, in the circuit arrangement described herein, deactivating means for deactivating the means CM when the control unit is in the conducting state, corresponding to the switched-on converter, which has the advantage that unnecessary power dissipation is counteracted. The functioning of the deactivating means is voltage-dependent and self-regulating.
The known circuit arrangement does not include a provision enabling the control unit to receive a signal under conditions corresponding to a defective incandescent lamp. This constitutes a problem for the application of the circuit arrangement and the semiconductor light source provided with said circuit arrangement.